Design Analysis and Fatigue Life of a Leaf Spring Assembly
Kuahal R
1, Jayaram A S
2, Chandan R
31
Student, Master of Technology, Dept. of Mechanical Engineering, Dr. Ambedkar Institute of Technology,
Bangalore, Karnataka, India
2
Associate Professor, Dept. of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bangalore,
Karnataka, India
3
Assistant Professor, Dept. of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bangalore,
Karnataka, India
---***---Abstract -The suspension system of an automobile is requiredto withstand harsh working conditions while performing its function of absorbing shocks .The Leaf spring is widely used in automobiles and one of the components of suspension system. It needs to have high fatigue life. The leaf spring of suspension system is subjected to cyclic stresses due to road undulations. As a general rule, the leaf spring is regarded as a safety component as failure could lead to severe accidents. In the present paper Structural Design validation analysis is performed by static, modal and fatigue loading conditions. Model of the leaf spring is performed using SOLID EDGE, then Imported to ABAQUS/CAE and mesh the leaf spring using Hexahedron elements, wedge elements are used to mesh wedge surfaces for fine meshing. Static analysis is performed to find deflection and stress of the leaf spring assembly. To study the dynamic behavior of the leaf spring assembly modal analysis is performed to find its natural frequency. This shows the stiffer suspension of leaf spring assembly. Fatigue life of leaf spring is analyzed by using FE-SAFE fatigue analysis software for both medium steel alloy and EN47 material of two different ultimate tensile strength. Substantial increase in life cycles is observed by using EN47 material. So the design is safe when we use the EN47 is used.
Key Words: Leaf spring, Static analysis, Modal analysis,
Fatigue life
1. INTRODUCTION
Leaf springs are mainly used in suspension systems to absorb shock loads in automobiles like light motor vehicle, heavy duty trucks and in rail systems. It carries lateral loads, longitudinal loads, side loads, brake torque, driving torque. Initially it called as laminated or carriage leaf spring. Leaf Spring is a simple form of spring commonly used for the suspension in wheeled vehicles. It is additionally perhaps the one of the most established type of springing, going back to medieval occasions. Sometimes referred to a semi elliptical spring or cart spring. It takes the shape of a slender arc-shaped length of spring steel of rectangular cross-section. The middle of the arc provides location for the shaft, whereas tie holes are provided at either end for attaching to the vehicle body. For automobile vehicles, by combining several leaves stacked on top of each other in many layers by which leaf spring can be made, often with progressively shorter leaves. A leaf spring can either be attached directly to the frame at both ends or attached directly at one end,
usually the front, with the other end attached to a shackle, a short swinging arm. For softer springiness the leaf spring elongates when compressed. Some springs terminated in a concave end, called a spoon end (seldom used now), to carry a swiveling member. The leaf spring mainly consists of different parts like Master leaf, Center bolt, central clamp, Eye, and Rebound clip. The leaf spring assembly is one of the main concerns for weight reduction in automobile as it accounts for 10-20% of the un-sprung weight.
Leaf spring absorbs vertical vibrations and impacts because of load irregularities by means that of variation within the spring deflection show that potential energy is hold on in spring as strain energy and so unleash slowly so, increasing energy stored capability of a leaf spring insures a better suspension system. The huge vehicle needs a decent suspension framework that can convey a decent ride and taking care of to the drivers while driving. At the same time that component needs to have high fatigue life to resist more jerks while running.
2. Aim
The main aim of this project is to determine the stress distribution, modes of vibration and Fatigue life of leaf spring assembly.
3.METHODS AND METHODOLOGY
The assessment of the Leaf spring assembly is considered for the evaluations. The design is evaluated for tension load condition of 4 kN. The stress distribution is studied. Further analysis is performed for static analysis, modal analysis and fatigue life of leaf spring. Load conditions for all the tests are as per standards applicable.
STEP 1:Create Leaf spring design using SOLID EDGE.
STEP 2: Import to ABAQUS/CAE and mesh the leaf spring assembly using Hexa elements.
Step 3: Performing linear static analysis using ABAQUS/Solver
4. GEOMETRIC MODELING
Fig -1: Front View of a Leaf Spring Assembly
Fig -2: Side View a leaf spring assembly
Fig -3: Isometric View a leaf spring assembly view
Fig -4: Cut section View a leaf spring assembly
4. MESHING
[image:2.595.62.561.66.672.2]Fig -5: Meshing
Table -1: Elements and Nodes Count
Total number of nodes 77916
Total number of elements 54055
Element type Linear Hexahedral
element
The FE modeling in linear hexahedral elements of type C3D8R as shown in above Fig 5. Since hexahedral elements have higher accuracy compared to other elements it has been used for meshing and 13 elements of linear wedge elements of type C3D6 has been used for wedge surfaces. Each element of hexahedral has 8 nodes and 6 faces. A suitable finer element size is used to capture the bending and static deflection in the structure. Free meshing techniques are common meshing technique in ABAQUS and use hexahedral element to obtain the accurate and DOF.
5. MATERIAL PROPERTIES
Most common important aspect is to check whether Leaf spring assembly withstands the load by applying material properties at pre-processing step. Here the material properties were applied while meshing.
Table -2: Material property for EN47 material
Sl. No Properties value
1 Density 7800 kg/m3
2 Young’s Modulus 205 GPa
3 Poisson’s Ratio 0.29
[image:2.595.60.258.585.734.2]For EN47 material good wear and abrasion resistance characteristics are often obtained by oil hardening and tempered condition. Processed EN47 material offers excellent shock resistance and toughness hence it is suitable material for the parts exposed to stress, shock and vibration. EN47 is utilized broadly in the automobile industry and many general designing applications. For the material with high tensile strength and toughness EN47 is preferred. Important applications of the EN47 include crankshafts, steering knuckles, gears, spindles and pumps.
Table -3: Material property for medium alloy steel material
Sl no Properties Value
1 Yield strength 338.8 Mpa
2 Ultimate strength 621 Mpa
3 Pulsating strength 500.3 Mpa
4 Alternating strength 279.5 Mpa
6. Loads and Boundary Conditions
Fig -6: Loads and Boundary Conditions
The output results of FEA is govern by the application of boundary conditions and loading condition, loads or forces, acceleration or deformations applied to a structure or its components. Deformations, displacement and stress in structures are caused by the applying load conditions. Boundary condition is the necessary constraints that must be applied to the particular order of problem to obtain the required solution. Boundary value problem can be solved as set of boundary conditions are known. Boundary conditions are the major factor for the output of the solution. The boundary condition is shown in Fig 6 and leaf spring assembly is fixed at radial and theta tangential direction, hence no rotational and translational motion
7. RESULT AND DISCUSSION
The analysis of the leaf spring assembly was carried out with loads and boundary conditions. The results obtained from static stress analysis (stresses and displacement) modal analysis and fatigue analysis is shown below.
[image:3.595.319.546.86.240.2]7.1 Static Analysis Results
Fig -7: Static Analysis
[image:3.595.44.279.351.497.2]The model subjected static analysis to determine the maximum deflection shown in the Fig .7 Maximum deflection of 0.34mm can be observed at the center of the leaf spring shown in Fig.7 by the applied load condition of 4kN. Maximum stress of 125.5 Mpa can be observed at the roots of the bearing hub. Stress at the bolt load point is 49 Mpa can be observed in Fig. 8 this shows the factor of safety around 7 which shows higher margin of safety.
Fig -8: Maximum Stress 7.2. Modal analysis
Mode shape and natural frequency of mechanical system can be determined by using modal analysis. In the frequency domain the figures indicates four different modes of vibrations the dynamic properties are studied by analyzing the different modes. To obtain better results the model created is incorporated to the ABAQUAS solver.
7.2.1. Bending mode (1st Mode)
Fig -9: Bending mode
[image:3.595.315.545.355.495.2]The 1st modes of vibration shown in Fig. 9 plotted to obtain independents from applied load; the nature frequency obtained is 92.953 Hz.
[image:4.595.321.541.133.327.2]7.2.2 Twisting mode (2nd Mode)
Fig -10: Twisting mode
The 2nd mode of vibration the natural frequency is 123.19Hz.which represented as twisting mode in Fig. 10
[image:4.595.39.281.150.294.2]7.2.3 Lateral Twisting mode (3rd Mode)
Fig -11: Lateral Twisting Mode
In the 3rd mode of vibration as natural frequency of 192.30Hz.which represented as lateral twisting mode in Fig. 11
7.2.4 Bending mode (4th Mode)
Fig -12: 2nd Bending Mode
In the final mode i.e. in the 4 th mode of vibration the natural frequency is 327.7Hz. From the above results, finally it can be concluded that 1st mode natural frequency is found to be
92.953 Hz. This is above the normal range of 30Hz which indicates a stiffer suspension of the leaf spring assembly.
[image:4.595.43.278.363.503.2]7.4 Fatigue Life Analysis
Fig -13: Fatigue life of medium alloy steel
Fatigue life of medium steel alloy is as shown in Fig. 13 the ultimate strength of medium steel alloy is 621Mpa. Maximum stress is observed at the roots of the bearing hub. It shows the minimum fatigue life cycle of 3728.
Fig -14: fatigue analysis of EN47 material
Fatigue life of medium steel alloy is as shown in fig 3.7.The ultimate strength of EN47 material is 880 Mpa. It shows the minimum fatigue life cycle of 107. Material change has been taken into consideration so that life of leaf spring will be improved.
8. CONCLUSIONS
The structural design validation analysis is performed by static, modal and fatigue loading conditions.
[image:4.595.324.541.404.586.2] [image:4.595.39.283.566.711.2] To study the dynamic behavior of the leaf spring assembly, modal analysis is carried out to check the natural frequency of the system. The first mode is observed at 92.935 Hz which shows a stiffer suspension to absorb shocks in road conditions.
To check the fatigue life of the system, the system is analyzed for spring steel with two different ultimate tensile strength limits. One with 621 Mpa and another with 880 Mpa. The EN47 material spring steel with 880 Mpa shows minimum fatigue life cycle of 107, whereas the earlier shows minimum cycles of 3728. So the design is safe when EN47 is used.
8.1 Scope of Future Work
Stress analysis may generate results which could assist in modification of the leaf spring structure for better performance.
Results are discussed as shown above and based on which conclusions are made by analysis above results we can further use these data’s and experiments in future for different conditions and material.
Fatigue analysis can be extended to other leaf spring and for different components.
By changing the material and its properties to determine the stress and fatigue analysis in improved manner.
The graduated leaf spring numbers can be varied.
By optimizing the thickness of the leaf spring for the required load conditions.
9. REFERENCES
[1] E Giannakis1, M Malikoutsakis1and G Savaidis1 “Fatigue Design of Leaf Springs for New Generation Trucks” Materials Science and Engineering volume 161 (2016) 012065
[2] Rushikesh S Pande1, Dhanaji R Jadhav2, C S Kodarkar3 “Fatigue and Design Analysis of Multi Leaf Spring” Vol. 6, Issue 5, May 2017.
[3] Dev Dutt Dwivedi1, V. K. Jain2 “review paper on design and fatigue analysis of leaf spring for automobile suspension system” issn (print): 2393-8374, (online): 2394-0697, volume-3, issue-1, 2016.
[4] V.K.Aher1, R.A.Gujar2, J.P.Wagh3 & P.M.Sonawane4 “Fatigue Life Prediction of Multi Leaf Spring used in the Suspension System of Light Commercial Vehicle” ISSN (Print): 2319-3182, Volume-1, Issue-1, 2012.
[5] Santosh Krishnaji Sindhe1, S. G. Bhatwadekar2, V. V. Kulkarni3, Satish Mullya4 “Static, Modal and Fatigue Life Prediction through CAE for a Leaf Spring used in Light Commercial Vehicle” Volume 2 Issue 3, March 2013.
[6] Pushpendra Shekhawat , 2. Gaurav Saxena, 3. Janmit Raj “Study on Static Structural Analysis of Parabolic Leaf Spring Used In Heavy Commercial Vehicle: A Review” © 2018 JETIR July 2018, Volume 5, Issue 7.
[7] A. Raveendra, Mohammed Abdul Mubashir “Design and Analysis of Leaf Spring for Heavy Weight Vehicles using Composite Materials” ISSN: 2278-3075, Volume-8 Issue-2S December, 2018.
[8] M Senthil Kumar1,* and S Vijayarangan2 “Static analysis and fatigue life prediction of steel and composite leaf spring for light passenger vehicles” Journal of Scientific & Industrial Research Vol 66, February 2007, pp 128-134.
[9] Jayesh Raj Pal1, Arun Singh Kushwah2 “Design and Optimization of Multi-Leaf Spring by Finite Element and Grey Relation Method” ISSN: 2321-9653; IC Value: 45.98; SJ Impact Factor:6.887 Volume 5 Issue IX, September 2017.
[10] Kumar Krishan and Aggarwal M.L. “A Finite Element Approach for Analysis of a Multi Leaf Spring using CAE Tools” Vol. 1(2), 92-96, Feb. (2012).
[11] Dhiraj Bhargav. A. S1, A. S. Jayaram2, Chandan. R3, “ DESIGN AND ANALYSIS OF ALLOY WHEEL FOR MULTI-PURPOSE VEHICLE” Volume: 05 Issue: 10 | Oct 2018 p-ISSN: 2395-0072
[12] Preetham Raj V1, Chandan R2, Doddanna K3, “ Stress Analysis and Fatigue Failure of Typical Compressor Impeller” Volume: 05 Issue: 10 | Oct 2018, p-ISSN: 2395-0072
[13] Lokesha1, Chandan R2, Byregowda K C3, “ Design and Structural Analysis of Cylindrical Shell”, Volume: 04 Issue: 09 | Sep -2017, p-ISSN: 2395-0072
